Identity
Identity is the sign-in service that issues the tokens every API, the OpenStack CLI and the OpenStack SDKs use.
Identity is where you sign in. It checks who you are and gives you a token, which every other service accepts, so you never sign in to a service separately. Identity also lists where each service is, in the service catalog.
Identity is OpenStack Keystone, so any tool that works with OpenStack can sign in with it at
https://auth.vexxhost.net/v3.
Concepts
Authentication
How tokens prove who you are, what they are valid for, and when they expire.
Projects
How a token's project decides which resources you see and change.
Service catalog
How tools find each service's endpoint in every region.